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A 2 yo male presents with a progressive limp for 2 days and he is now refusing to bear weight. He has had fevers for 24 hours with a Tmax of 103 and an otherwise negative review of systems. On exam his thigh is abducted and externally rotated. The child screams with any movement of his lower extremity. What 2 tests will help you most in confirming your suspected diagnosis?

Plain films and WBC

Blood culture and WBC

ESR and WBC

Blood culture and ESR

ANSWER:3. This patient most likely has either transient synovitis or a septic hip – fever, limp and thigh abducted and externally rotated. The Kocher Criteria are a set of 4 criterion to help differentiate between transient synovitis and septic arthritis of the hip. They are:

Inability to tolerate weight bearing

Fever > 38.5 C (101.3 F)

ESR > 40mm/hr

WBC > 12,000 cells/mm3

If all 4 are present the probability of septic arthritis is 99.6%, if 3 probability is 93.1% and if only 2 are present the probability drops to 40%. While plain films and a blood culture are not inappropriate, they will most likely not be helpful in confirming the diagnosis. PEARL: Differentiate between transient synovitis and septic arthritis of the hip using the Kocher Criteria. 1) Inability to tolerate weight bearing, 2) Fever > 38.5 C (101.3 F), 3) ESR > 40mm/hr and 4) WBC > 12,000 cells/mm3. ARTICLE:Kocher et al. Differentiating between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm. JBJS 1999 Dec: 81(12):1662-70.BACKGROUND: A child who has an acutely irritable hip can pose a diagnostic challenge. The purposes of this study were to determine the diagnostic value of presenting variables for differentiating between septic arthritis and transient synovitis of the hip in children and to develop an evidence-based clinical prediction algorithm for this differentiation.METHODS: We retrospectively reviewed the cases of children who were evaluated at a major tertiary-care children's hospital between 1979 and 1996 because of an acutely irritable hip. Diagnoses of true septic arthritis, presumed septic arthritis, and transient synovitis were explicitly defined on the basis of the white blood-cell count in the joint fluid, the results of cultures of joint fluid and blood, and the clinical course. Univariate analysis and multiple logistic regression analysis were used to compare groups. A probability algorithm for differentiation between septic arthritis and transient synovitis on the basis of independent multivariate predictors was constructed and tested.RESULTS: Patients who had septic arthritis differed significantly (p < 0.05) from those who had transient synovitis with regard to the erythrocyte sedimentation rate, serum white blood-cell count and differential, weight-bearing status, history of fever, temperature, evidence of effusion on radiographs, history of chills, history of recent antibiotic use, hematocrit, and gender. Patients who had true septic arthritis differed significantly (p < 0.05) from those who had presumed septic arthritis with regard to history of recent antibiotic use, history of chills, temperature, erythrocyte sedimentation rate, history of fever, gender, and serum white blood-cell differential. Four independent multivariate clinical predictors were identified to differentiate between septic arthritis and transient synovitis: history of fever, non-weight-bearing, erythrocyte sedimentation rate of at least forty millimeters per hour, and serum white blood-cell count of more than 12,000 cells per cubic millimeter (12.0 x 10(9) cells per liter). The predicted probability of septic arthritis was determined for all sixteen combinations of these four predictors and is summarized as less than 0.2 percent for zero predictors, 3.0 percent for one predictor, 40.0 percent for two predictors, 93.1 percent for three predictors, and 99.6 percent for four predictors. The chi-square test for trend and the area under the receiver operating characteristic curve indicated excellent diagnostic performance of this group of multivariate predictors in identifying septic arthritis.CONCLUSIONS: Although several variables differed significantly between the group that had septic arthritis and the group that had transient synovitis, substantial overlap in the intermediate ranges made differentiation difficult on the basis of individual variables alone. However, by combining variables, we were able to construct a set of independent multivariate predictors that, together, had excellent diagnostic performance in differentiating between septic arthritis and transient synovitis of the hip in children.

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